The present invention relates to an ultrasonic transducer which is used in ultrasonic diagnosing apparatus, for transmitting and receiving ultrasonic waves.
Heretofore, studies for allowing an ultrasonic transducer to have a frequency characteristic over a wide range, and to have a structure using an acoustic lens have been made. For example, a structure disclosed in Handbook of Medical Ultrasonic Equipments, page 186. "5.3.1 Basic Structure of Ultrasonic Probe", has been well-known.
FIG. 5 shows a conventional ultrasonic transducer of this kind, which comprises a piezoelectric element 11 having a uniform thickness, at least two ultrasonic matching layers 12, 13 provided on the ultrasonic wave transmitting and receiving side (front surface side) of the piezoelectric element 11 and having a uniform quarter wave length thickness, for relaxing reflection caused by mismatching in acoustic impedance between the piezoelectric element and an object to be detected, so as to effectively radiate ultrasonic waves, a backing member 14 provided at the rear surface of the piezoelectric element 11 so as to have damping and holding functions, and an acoustic lens 15 provided at the front surface of the acoustic matching layer 13 and made of silicone rubber materials, for converging an ultrasonic beam.
The above-mentioned arrangement can have a frequency characteristic having a wide band, and further, can materialize a high resolution since the ultrasonic wave is converged thinly.
However, the conventional ultrasonic transducer having the above-mentioned arrangement has offered problems such that ultrasonic signals transmitted to or received from an object to be detected dampen so as to remarkably deteriorate its frequency characteristic in a high frequency range since the attenuation coefficient of the acoustic lens 15 made of silicone rubber materials or the like is high, and such that the sensitivity (efficiency) is remarkably deteriorated due to the attenuation through the acoustic lens 15.